DESCRIPTION (from applicant's abstract): The long-term research objective of this project is to characterize, in molecular terms, the circadian oscillator of Drosophila. Previous studies from this laboratory have shown that PER and TIM proteins interact in vivo and that this complex disassociates in response to light. They have also shown that the disruption of the cytoplasmic PER-TIM complex is associated with a delay in PER phosphorylation and PER nuclear entry. The specific aims of this current application are to: (1) Characterize trans-acting factors and cis-acting elements that participate in the post-transcriptional control of per mRNA levels, (2) Determine the role of PER, TIM and dCLOCK phosphorylation and identify in vivo partners of PER and TIM, and (3) Characterize the spatial and temporal regulation of dCLOCK expression and determine how PER and TIM interact with the dCLOCK-CYC complex.